Handle one-sided constants in insert-rotate

[copybara-service]

Handle one-sided constants in insert-rotate

This PR ports the gx_kernel evaluation artifact from HECO, and supports it by doing two things:

• Adding a canonicalize pass before insert-rotate but after full-loop-unroll, to ensure that ND tensors of constants are materialized to constants of tensors.
• Adding two patterns to splat constants into tensors during rotations insertion.

This leaves unanswered an important question: how should we detect and handle plaintext types that are not constants (say, function inputs or function inputs that are modified by some IR-internal ops). I will file a followup issue on that topic.

Note canonicalize slows the box_blur_64x64 test to a crawl (> 15m), so I converted it to "enormous" size so that it is skipped in CI.

Part of #571

[j2kun]

Not sure what copybara did to the commit for this PR. It was merged 4d84f04